The present invention relates to a film-forming apparatus that forms an optical film on optical members by sputtering in a vacuum apparatus with an adjustable reduced pressure atmosphere, to a method therefor and to film-formed substrates with films formed thereby.
It has been attempted in the past to place two sputtering targets adjacently on the same plane on respective cathodes, and coat the substrate with a coating comprising the components of the target material. In such cases, the method adopted is to provide each cathode with a power source for application of a negative voltage to the cathodes, i.e., to supply a negative voltage to each cathode with electrically separate systems.
This has been developed in recent years into an apparatus such as shown in FIG. 13, where alternately reversed voltages are applied to two targets on the same plane and a film is formed on a substrate while destaticizing the targets.
In the abbreviated cross-sectional view of a film-forming apparatus shown in FIG. 13, argon gas or, if necessary, oxygen, nitrogen, methane, alcohol, a hydrocarbon, fluorocarbon or other gas is introduced into the film-forming apparatus through a gas introduction tube (not shown), while the inside of the film-forming apparatus is simultaneously evacuated with an evacuation pump (not shown) to prepare a space reduced to a given pressure; when a negative voltage is applied from the power source 7 to the cathodes 1A, 1B arranged in a row, the glow discharge plasma 3 produced on the surface of the respective targets 2A, 2B situated on each cathode 1A, 1B accomplishes sputtering of the target 2A and the target 2B. When the cathode 1A is a positive electrode, the cathode 1B is a negative electrode. When the cathode 1A is a negative electrode, the cathode 1B is a positive electrode.
A gas retainer plate/anti-adhesion plate/film thickness control plate 6 is mounted surrounding the two cathodes 1A, 1B, and this prevents unnecessary flying of the sputtered particles while also closing off spread of the plasma 3 to stabilize the process. A substrate 4 on which the film is to be formed is situated at a position opposite the target 2A and target 2B outside the openings of the gas retainer plate/anti-adhesion plate/film thickness control plate 6. The substrate 4 is conveyed in the same direction as the direction in which the pair of targets 2A, 2B are oriented.
A magnetron power source 7 applies a negative voltage to the cathodes 1A and 1B. At this time, an oscillator, switching circuit or AC electric generator 8 alternately reverses the polarity of the cathodes 1A and 1B so that the cathode 1B is the positive electrode when the cathode 1A is the negative electrode and so that the cathode 1A is the positive electrode when the cathode 1B is the negative electrode, to destaticize the charge accumulated on the surface of the targets 2A, 2B, while from an instantaneous point of view, the alternating reverse glow discharge plasma 3 produced by applying a negative voltage to one of the cathodes 1A or 1B and a positive voltage to the other of the cathodes 1B or 1A causes sputtering of the targets 2A and 2B situated on the surfaces of the two cathodes 1A and 1B.
On the other hand, there are methods for forming films on the ends of optical three-dimensional parts by vacuum evaporation, whereby films can be coated on the ends or sides of numerous small optical (three-dimensional) parts, which uses the combined effect of rotating a dome loaded with the optical parts and using activating means such as a plasma assist.
Problems to be Solved by the Invention
There has been a limit to the number of optical parts that can be charged by the aforementioned optical part vacuum evaporation process, and productivity has not been very high.
In addition, there are also limits on the materials that can be used for conventional film formation by such vacuum evaporation, and in principle compounds comprising elements of different vacuum evaporation pressures have different vacuum evaporationization rates for each element, such that composition of the vacuum evaporation source has often differed from the composition of the film.
It is an object of the present invention to provide a film-forming method for fabrication of compact optical parts using a bell jar (or xe2x80x9ccarousel-shapedxe2x80x9d) apparatus whereby the number of parts that can be placed in the apparatus at a time can be increased, and to provide an apparatus therefor.
The aforementioned objects of the invention can be achieved by the following construction.
(1) A film-forming apparatus comprising a magnetron sputtering cathode, a target situated on the cathode and a film-forming substrate positioned opposite the target, in a vacuum apparatus with an adjustable reduced pressure atmosphere, the film-forming apparatus characterized by being provided with a pair of cathodes located proximally to each other and situated in a straight line in the direction perpendicular to the conveying direction of the substrate, with at least one row situated in the conveying direction of the substrate, and a power source device (a power source, an oscillator, switching circuit or AC electric generator etc.) that alternately reverses the polarity of the pair of cathodes so that when the first of the pair of cathodes is used as a negative electrode the second of the pair of cathodes is used as a positive electrode, and when the second of the pair of cathodes is used as a negative electrode the first of the pair of cathodes is used as a positive electrode, in order to apply a glow discharge-producing voltage to a pair of targets corresponding to each of the pair of cathodes, situated on the surface of each cathode.
(2) A film-forming method in which a magnetron sputtering cathode, a target situated on the cathode and a film-forming substrate positioned opposite the target, are situated in a vacuum apparatus with an adjustable reduced pressure atmosphere, to form a film on the surface of the substrate, the film-forming method being one which comprises situating a pair of cathodes located proximally to each other in a straight line in the direction perpendicular to the conveying direction of the substrate, with at least one row situated in the conveying direction of the substrate, alternately reversing the polarity of the pair of cathodes so that when the first of the pair of cathodes is used as a negative electrode the second of the pair of cathodes is used as a positive electrode, and when the second of the pair of cathodes is used as a negative electrode the first of the pair of cathodes is used as a positive electrode, in order to apply a glow discharge-producing voltage to a pair of targets corresponding to each of the pair of cathodes, situated on the surface of each cathode, and simultaneously sputtering the pair of targets by the produced glow discharge to form a film comprising the structural material of the targets on the surface of the substrate.
(3) A film-formed substrate characterized by being obtained by the film-forming method of (2) above.
It is preferred to provide an oscillator, switching circuit or AC electric generator between the power source and cathodes for alternate reversal of the polarity of the pair of cathodes. In the film-forming apparatus of the invention, as shown by the plan view of the surfaces of the targets 2A, 2B in FIG. 1, the pair of targets 2A, 2B are situated adjacent to each other and they are arranged serially in the direction perpendicular to the conveying direction, with at least one row situated in the conveying direction of the substrate 4.
The film-forming apparatus of the invention, in which the pair of targets 2A, 2B are situated adjacent to each other and they are arranged serially in the direction perpendicular to the conveying direction, with at least one row situated in the conveying direction of the substrate, alternately reverses the polarity of the cathodes 1A, 1B corresponding to the pair of targets 2A, 2B, so that the polarity of each of the targets 2A, 2B is alternately reversed when the voltage is applied; this method allows a coating to be formed on the surface of the substrate 4 by glow discharge sputtering, to accomplish destaticizing while the sputtering can be carried out using a small in-line or bell jar (or xe2x80x9ccarousel-shapedxe2x80x9d) apparatus with a small space.
In contrast, in the film-forming apparatus shown in FIG. 13, the targets 2A, 2B situated for the pair of cathodes 1A, 1B whose polarities are alternately reversed are oriented in the same direction as the conveying direction of the substrate 4 so that the film-forming apparatus requires a relatively large space.
As the bell jar apparatus mentioned above, seen in FIG. 2 (FIG. 2(a) shows a view of the bell jar apparatus in the horizontal cross-sectional direction, with the rotating axis in the vertical direction, and FIG. 2(b) shows an expanded side view of each target section of FIG. 2(a)), there may be used a film-forming apparatus having a substrate 4 that is rotatably situated around the center of one rotating axis 10 at the vertical direction in an inner cylinder 12, and a plurality (four in FIG. 2) of target units each comprising the pair of targets 2A, 2B (2B is under 2A and cannot be seen in FIG. 2) serially arranged in the vertical direction inside an outer cylinder 13 opposite the surface 4a of the substrate 4, which are arranged in parallel in the circumferential direction of the inner wall of the outer cylinder 13. FIG. 2(b) shows an expanded side view of the targets 2A, 2B, and a backing plate 14 and magnetron magnet 15 are situated behind the targets 2A, 2B.
The film-forming apparatus of the invention may also have the construction shown in FIG. 3 (FIG. 3(a) is a plan view of the targets 2A, 2B from the side of the magnets 15A, 15B on the backing plates 14A, 14B respectively and FIG. 3(b) is a side view of the targets 2A, 2B), wherein the magnetron magnet 15 on both of the backing plates 14A and 14B is situated so that the average magnetic force at the border section between the pair of targets 2A, 2B situated adjacent to each other is weaker than at the other sections, and so that the magnetic field at the erosion zones (the zones where sputtering is performed) on the targets 2A, 2B are equivalent at the sections near the border section and at the other sections. The method whereby the average magnetic force at the border section is rendered weaker than at the other sections may involve, for example, the use of a magnetron magnet 15 with a weaker magnetic force at the border section than at the other sections, or it may be achieved by constructing the magnetron magnet 15 at the border section with magnets 15 consisting of numerous small strips arranged in a row, and making adjustment by increasing or decreasing the spacing between the small strips of magnets 15.
The aforementioned film-forming apparatus may also have the construction shown in FIG. 4 (FIG. 4(a) is a plan view of the targets 2A, 2B from the side of the magnet 15 and FIG. 4(b) is a side view of the targets 2A, 2B), wherein magnetron magnets 15 forming a single continuous magnetic circuit may be arranged in the pair of targets 2A, 2B.
The construction may be such that the difference in the target film thickness in the direction perpendicular to the conveying direction of the substrate 4 obtained by the process of sputtering the entirety of the pair of targets 2A, 2B shown in FIGS. 2 to 4 is within a range of about xc2x120%, and preferably within a range of about xc2x110%, in the main film-forming region.
Providing the magnetron magnet 15 causes the electrons to be trapped within the magnetic field on the targets 2A, 2B, and therefore gas such as argon that is supplied to the apparatus is ionized to a high density and impacts with the targets 2A, 2B at a high acceleration. This greatly increases the sputtering efficiency.
As shown in FIG. 5 (FIG. 5(a) is a schematic drawing of a construction in which an optical monitor is mounted on a bell jar film-forming apparatus, and FIG. 5(b) is a view along arrow Axe2x80x94A of FIG. 5(a)), an optical detector 17 such as an optical film thickness meter utilizing a light interference effect or the like may be installed on the side wall of a bell jar film-forming apparatus 13, and the accumulated film thickness and film transmission spectrum may be measured during the actual formation of the film on the substrate 4 from the targets 2A, 2B. A film thickness monitor employing a crystal oscillator may also be used instead of an optical detector 17, in which case the output of the crystal oscillator may be fed back to the power source to stably control the film-forming speed.
Here, as shown in FIG. 5, the end of the optical system of the optical detector 17 is situated with its optical axis in the direction normal to the side wall of the cylinder of the bell jar film-forming apparatus 13 (the direction perpendicular to the rotating axis 10 of the film-forming apparatus 13).
The film thickness may be adjusted by controlling the power source voltage, etc. with a film formation controlling system 18 while measuring the accumulated film thickness and transmission spectrum in the film formed on the surface of the substrate 4 (detecting the transmission spectrum by installing the light source on the side opposite the accumulated film transmission spectrum detector).
As shown in FIG. 6 (FIG. 6(a) is a schematic view of an construction in which a crystal film thickness meter is mounted inside a bell jar film-forming apparatus and FIG. 6(b) is a view along arrow Axe2x80x94A of FIG. 6(a)), a crystal film thickness meter 20 utilizing the mass change effect is installed near the front of the targets (cathodes) 2A, 2B, the signal corresponding to the accumulation rate of the film during actual film formation on the substrate 4 is measured, the signal is sent to a film formation control system 21 and a signal for control of the power of the power source of the cathode to keep the film accumulation rate at the prescribed value is sent to the power source so that the prescribed film accumulation rate may be stably maintained; it is thus possible to stably obtain a constant film thickness if the conveying speed or rotating speed of the substrate 4 is constant.
As shown in FIG. 7 (FIG. 7(a) is a schematic view of a construction in which an optical detector for detection of plasma emission is mounted on a bell jar film-forming apparatus, and FIG. 7(b) is a view along arrow Axe2x80x94A of FIG. 7(a)), an optical detector 22 capable of detecting plasma emission during film formation is installed near the film-forming apparatus, and the construction may be such that the optical detector 22 with one or more plasma emission-detecting optical axes is situated in a plane parallel to the surface of the targets 2A, 2B so that the reaction rate between the reactive gas and the flying particles from the targets 2A, 2B is controlled to the desired stable value.
Thus, the construction may be such that the intensity of the detected plasma emission is transmitted to the film-forming control system 23, and each of the targets 2A, 2B is provided with one or more systems with a mechanism that sends a control signal, based on the difference between this intensity and the value previously given by the user to the film-forming control system 23 which is necessary to maintain the two in a fixed relationship, from the film-forming control system 23 to a process gas flow control valve with a piezo-movable mechanism.
A film may also be formed at a low film-forming speed and high stability in reactive mode, without using plasma control. For this purpose it is preferably carried out in the reactive region of the hysteresis graph of the voltage plotted against the oxygen flow ratio.
By providing the film-forming apparatuses and film formation control systems 18, 21, 23 shown in FIGS. 5 to 7 above, it is possible to realize rapid, stable and precise coating of optical films on microparts, for example.
When a bell jar film-forming apparatus such as shown in FIG. 5 to FIG. 7 is used, the number of optical parts that can be placed in the apparatus at a time can be increased, and the space for management of the non-film-formed sections such as optical fibers can be provided inside the bell jar.
According to the invention, the material for the targets may be of a single type, and as target materials there may be used metals and inorganic elements composed mainly of conductive materials such as Al, Si, Ti, Nb, Zn, Sn, Zr, In, Bi, Ta, V, Cr, Fe, Ni, Ce and C, as well as their alloys and suboxides. Oxides or nitrides of these target materials can be accumulated onto the substrate 4 in one or more layers by reactive sputtering using oxygen or nitrogen.
Experimentally, C targets have been used by mixing an organic carbon compound gas such as methane with argon or the like and introducing them for plasma conversion to stably obtain diamond-like carbon films or carbon hydride films at low temperature and with high density and hardness. This has allowed stable coating of dense dielectric materials or protective film materials at a rapid speed.
Moreover, oxides of the aforementioned metals and inorganic substances composed mainly of Al, Si, Ti, Nb, Zn, Sn, Zr, In, Bi, Ta, V, Cr, Fe, Ni, Ce and C, or compound oxides or nitrides of a plurality of these metals may be used as target materials, and targets whose surface resistance is no greater than surface resistance 1 K-ohm can be accumulated on the substrate 4 to one or more layers by sputtering carried out using mainly argon. This method allows dielectric materials to be stably coated from ceramic targets.
Furthermore, when target layers are made with two or more different target materials and either one of these layers is obtained by the composition containing at least one type of metal of either In or Sn as an antistatic layer, it is possible to accumulate the In or Sn oxides by sputtering and thus rapidly and stably produce a coating with conductive and antistatic functions.
In addition, when target layers are made with two or more different target materials and either one of these layers is obtained by the composition containing at least one type of metal of Ti, Nb and Al as an antifouling layer, it is possible to accumulate the corresponding oxides of Ti, Nb and/or Al oxides by sputtering and thus form an optical multi-layer film with an antifouling effect due to a photocatalytic effect. For titania in particular, substances with an anatase crystal structure exhibit highly effective catalytic action.
The substrate for the invention may be a direct combination of a special substrate such as a rod lens, micro lens array, optical fiber or the like with an anti-reflection film or interference filter film formed by rapid and low-temperature sputtering having high activity, to increase its value as an optical part and thus lower production costs.
According to the present invention it is possible to obtain compact films and thus realize optical precision needed for optical parts that require precise standards.